As LCDs, one of many types of image displays, have been technically improved to provide wide viewing angles, high resolution, high response, good color reproduction, and the like, applications of LCDs are spreading from laptop personal computers and monitors to television sets. In a basic LCD structure, two flat glass substrates each provided with a transparent electrode are opposed via a spacer to form a constant gap, between which a liquid crystal material is placed and sealed to form a liquid crystal cell, and a polarizing plate is adhered on the outside surface of each flat glass substrates. In a conventional technique, a glass or plastic cover plate is attached to the surface of a liquid crystal cell in order to prevent scratches on a polarizing plate bonded to the surface of the liquid crystal cell because of low scratch resistance of the polarizing plate. However, the placement of such a cover plate is disadvantageous in terms of cost and weight. Thus, a hard-coating process has gradually been used to treat the surface of polarizing plates. The hard-coating process is commonly conducted in a way such that a hard coating film comprising a transparent plastic substrate on which a hard coating layer is formed is provided on a side of a polarizing plate.
Besides, in a case where a hard coating film is adhered onto various kinds of image displays, visibility of a display is reduced by light reflection on a display surface, which is on a polarizing plate surface. Hence, more improvement on visibility is required to a hard coating film. In particular, visibility can be significantly reduced by surface reflection in various personal digital assistances such as car navigation monitors, video camera monitors, cellular phones, and PHS, which are frequently used in outdoor environments. Therefore, polarizing plates generally undergo an antireflection treatment. Particularly, polarizing plates to be installed in the personal digital assistances have to undergo an antireflection treatment.
The antireflection treatment is designed to reduce reflection as much as possible in the visible light range and thus generally includes forming a multilayered structure of thin films different in refractive index or a monolayer structure of a low refractive index material by a dry process such as vacuum deposition, sputtering and CVD or by a wet process with a die or a gravure roll coater. In general, an antireflection layer (low refractive index layer) with a monolayer structure is industrially used, because it can be produced with no complicated process and allows a cost reduction.
In a conventional antireflection hard coating film, however, an antireflection layer is composed of a thin film with a thickness of 0.1 to 0.5 μm, and the interlayer adhesion is weak. Such a film can easily cause failure at the interface with the hard coating layer and has difficulty in achieving satisfactory film strength and durability such as chemical resistance.
LCD applications have come to include home television sets, and thus it is easily expected that the users of general home television sets should handle LCD television sets in the same manner as in the case of glass CRT television sets. Therefore, there has been a demand for antireflection hard coating films with further improved hardness and improved film strength and chemical resistance.
In order to improve the film strength and chemical resistance, there is proposed a method in which the adhesion at the interface between stacked hard coating layer and antireflection layer is increased by various surface-modifying processes such as a corona discharge treatment (see Patent Literature 1 below). After coating, the strength and chemical resistance of the antireflection layer can be improved by these modification processes. However, the hard coating layer can often be unevenly processed, and when an antireflection layer is formed thereon by coating, uneven coating can often occur, which provides a problem for antireflection properties.
There is also proposed an antireflection hard coating film that includes a high refractive index hard coating layer mainly produced from an ionizing radiation-curable resin containing a reactive organosilicon compound, so that the antireflection layer can have excellent adhesion to the high refractive index hard coating layer (see Patent Literature 2 below). According to Patent Literature 2, however, the reactive organosilicon compound makes up 10 to 100% by weight of the resin components of the hard coating layer, and thus it is difficult to achieve satisfactory adhesion and hardness at the same time.
Patent Literature 1: JP-A No. 09-222503
Patent Literature 2: JP-A No. 09-226062